1. Field of the Invention
The present invention relates to compositions and methods of treatment of depression or other affective mood disorders or pathological mental and/or emotional states, by administration to a subject suffering or susceptible to same, of delta opioid receptor agonist compound(s), optionally in combination with other agents.
2. Description of the Related Art
Depression is a difficult mental disorder to treat. Patients having such a disorder are often reluctant to seek the medical attention necessary to diagnose the disorder. Such reluctance is often related to the patient's fear of the stigma associated with seeking psychiatric help or to the patient's feeling of worthlessness associated with depression. Moreover, once the patients seek competent psychiatric help, it is difficult to successfully treat the disorder through a psychoanalytic approach alone.
In the Diagnostic and Statistical Manual of Mental disorders, Fourth Edition, (DSM IV) published by the American Psychiatric Association, depressive disorders are classified under mood disorders and are divided into three types: major depressive disorder, dysthymic disorder and depressive disorder not otherwise specified. Major depressive disorder and dysthymic disorder are differentiated based on chronicity, severity and persistence. In major depression, the depressed mood must be present for two weeks. In dysthymic disorder, the depressed mood must be present for two weeks. In dysthymic disorder the depressed mood must be present most days over a period of two years.
Usually, major depressive disorder is characterized by its sharp contrast to usual functioning. A person with a major depressive episode can be functioning and feeling normal and suddenly develop severe symptoms of depression. By contrast, a person with dysthymic disorder has chronic depression with less severe symptoms than major depression.
In an effort to treat depression, a variety of antidepressant compositions have been developed. Among these are the selective serotonin reuptake inhibitors (SSRI), such as sertraline (registered trademark ZOLOFT®—Pfizer), fluoxetine (registered trademark PROZAC®—Eli Lilly), paroxetine (trade name PAXIL®—Glaxo Smith Kline), and fluvoxamine (trade name LUVOX™). Other examples of antidepressant compositions include tricyclic antidepressants such as those sold under the registered trademark ELAVIL™ (Merck, Sharpe and Dohme); aminoketone antidepressants such as bupropion; and lithium, a metal used to treat bipolar disorder. However, these drugs are potent, often generating problematic side effects such as lethargy, clouded thinking, a lack of ability to concentrate, and sexual dysfunction. Often, these drugs take about six to eight weeks to exhibit any desirable therapeutic effects. This time period can be prolonged when the correct drug or combinations of drugs has to be determined, by trial and error before any therapeutic effects are observed. Furthermore, current research suggests that many of these drugs produce undesirable physiological side and it is also unknown how these drugs may affect pediatric and adolescent patients.
Therefore, what is needed is an effective, pharmacologically-based treatment for depression. It would also be desirable to have a treatment that potentiates the action and reduces the side effects of known compositions used in the treatment of depression. Such a method of treatment is lacking in the prior art.